In the continuing search for polymers suitable for use at elevated temperatures, many different repeating structures involving diverse connecting linkages have been suggested, e.g., aromatic structures connected by linkages such as imides, ethers, sulfones, ketones, etc. Unfortunately, as potential performance at elevated temperature has been enhanced, amenability of the polymer candidates to classical molten techniques of polymer fabrication has declined. More often than not, the same decline in melt processability accompanies attempts to produce temperature resistant polymers of elongation of at least about 50%, a necessary property for many polymer applications, e.g., if the polymer-insulated wire is to be capable of being twisted about itself without cracking of the insulation.
Aromatic polyketones, for example, are known to enjoy good resistance to thermal degradation. Bonner, in U.S. Pat. No. 3,065,205, suggested the Friedel-Crafts catalyzed polymerization of certain reactants to yield polyketones, listing as typical Friedel-Crafts catalysts ferric chloride and boron trifluoride. The reactants proposed fall into two classes, the first consisting of aryl ethers and polynuclear aromatic compounds, a member of which is heated with a member of a second class consisting of aliphatic and aromatic diacyl chlorides. The two basic reactions taught by this patent, then, can be summarized as follows:
(1) n(HR--O--RH)+n(Cl--A--Cl)+nHCl+H(R--O--R--A).sub.n Cl PA1 (2) n(HBH)+n(Cl--A--Cl)+nHCl+Cl(A--B).sub.n H
where HBH is a polynuclear aromatic hydrocarbon such as naphthalene, HR--O--RH is an ether such as diphenyl ether, and Cl--A--Cl is a diacyl chloride such as terephthaloyl chloride or phosgene. When phosgene and diphenyl ether are allowed to react, the resulting polymer will contain the repeating unit ##STR2##
An entirely different approach is taken by Farnham and Johnson in British Pat. No. 1,078,234 (corresponding to U.S. application Ser. No. 295,519, filed July 16, 1963). Here, polyarylene polyethers are produced by reaction of an alkali metal double salt of a dihydric phenol with a dihalo benzenoid compound. The dihydric phenol may contain a keto group--thus, 4,4'-dihydroxy benzophenone is claimed to give rise to a polyketone (See claim 15 of British patent).
The same repeating unit is disclosed in British Pat. No. 971,227 to arise from the reaction of diphenyl ether with phosgene, from the polycondensation of diphenyl ether-4-carbonyl chloride, and from the reaction of diphenyl ether with diphenyl ether-4,4'-dicarbonyl chloride.
A number of patents dealing with improved methods of making polyketones have since issued. Thus, for example, processes disclosed in U.S. Pat. Nos. 3,441,538 and 3,442,857 derive advantage by resort to hydrogen fluoride-enhanced boron trifluoride catalysis, a system earlier recognized in Boron Fluoride and its Compounds as Catalysts, etc., Topchiev et al, Pergamon Press (1959), p. 122; J. Org. Chem. 26 2401 (1961); and I&E Chem. 43, 746 (1951). A further patent dealing with an improved process is British Pat. No. 1,086,021. The foregoing are incorporated herein by reference to illuminate the background of this invention.
Example 10 of British Pat. No. 971,227 describes a manufacturing process for the polymer of repeating unit ##STR3## The product showed no signs of flowing up to 350.degree. C. and apparently required spinning from solution for fiber formation. The product is also variously described in Example 1 of U.S. Pat. No. 3,441,538 as yielding polymer of low elongation and tough, opaque brown films, while in British Pat. No. 1,153,527 this polymer is characterized as highly crystalline and intractable from the standpoint of conventional melt fabrication.
From the foregoing it will appear that while this polymer of a basically simple repeating unit possesses characteristics which render it a feasible candidate for high temperature application, its intractability in heretofore realized embodiments has rendered it ill-suited to conventional melt processing. Thus, a need has existed for melt processable polyketones comprised of the repeating unit ##STR4## if its other advantages are to be fully utilized.
The manner in which these needs are solved is described in my copending application, Ser. No. 451,521 in which a process is described for controlling the molecular weight of the polymer of that repeat unit to achieve a melt-processable polymer. A similar process for obtaining a polymer of the repeat unit ##STR5## is described in my U.S. Pat. No. 3,914,298, issued Oct. 21, 1975, the disclosure of which is incorporated by reference.
These polymers are useful in many diverse applications where thermal stability is important.
Other highly aromatic polymers having different repeat unit promise many of the same advantages as polyaryl ketones. For example, polyaryl sulphones of structure ##STR6## are described in British Pat. No. 1,109,842. These polymers are made by the Friedel-Crafts polymerization of either ##STR7## or a mixture of ##STR8## where X is halogen.
Although a wide variety of highly aromatic polymers are known to the prior art as indicated by this discussion, there still remains unmet a need for a simple process to obtain such polymers in a form in which they are melt processable.